Electric cable.



LE ROY CLARK. ELECTRIC CABLE. APPLICATION FILED MAR.|0,1915.

1,231 ,568. Patented July 3, 1917.

LE ROY CLARK, 0F ENGLEWOOD, NEW JERSEY.

ELECTRIC CABLE.

Specification of Letters Patent.

Application filed March 10, 1915. Serial No. 13,484.

To all whom t may concern Be it known that I, LE ROY CLARK, a

citizen of the `Uni ed` States, residing at Englewood, in the county fBergen and State of New Jersey, have invented certain new and usefulImprovements in Electric of insulation such as rubber, rubber compounds,paper or cambric tape, or the like, and some of the beneficial resultswhich are derived from its use will be hereinafter specificallyenumerated, while others will be obvious to those skilled in the art.l

In the accompanying drawings there are shown two standard types of`cable equipped with metallic sheaths inaccordance with the invention,and the figures are intended to be illustrative of the construction ofthe sheath and not to limit the scope of the in' vention to the specifictypes of cables shown.

Figure l shows a length of a single conductor cable constructed inaccordance with the invention, portions of the insulation and sheathbeing broken away to clearly show the construction.

Fig. 2 is a transverse section through the cable shown in Fig. l; and` jFig.v 3 is a transverse section through a sector type of cable, showinga sheath incasing each of the three groups of strands forming the cable.

In the form of cable shown in Figs. l and 2 the single conductor lcomprises a plurality of individual wires 2 which are twisted togetherin the usual manner to provide a round conductor, although for thepurposes of this invention, instead of a single conductor a multipleconductor cable could be used consisting of a pluralty `of conductorstwisted together in thek same manner, each conductor comprising aplurality of twisted individual wires.

Surrounding the conductor l is a flexible sheath 3 which is formed bywinding a thin metallic ribbon or tape spirally around the entire lengthof the conductor preferably so that the edges of adjacent turns slightlyoverlap each other. lIn winding the ribbon around the conductor theturns are closely drawn and bound firmly to the conductor so that thejoints between the overlapping edges are practically liquid-tight. Inpractice, a thin metallic copper ribbon of five mils in thickness hasbeen` used with good results, the edges of the adjacent turnsoverlapping for about a quarter the width of the ribbon. By winding theribbon spirally around the cable, the flexibility of the cable is notimpaired, since a narrow ribbon-may be used with conductors of smalldiameter and the width of it increased for conductors of larger diameterwhere the arc upon which the conductor may be bent is relatively large.

A sheath of this character is of particular advantage. where a coatingof rubber or rubber compounds is used as the insulation. With existingforms of cable where the rubber is applied directly to the conductoritself, it has been found that since 'the rubberor rubber compoundswhich coat the conductor are applied toit when in soft condition andbefore vulcanizing, a considerable quantityv of the insulation is wastedin filling the spirally disposed spaces or grooves 4 which occur betweeneach pair of the exterior wires forming the conductor. When the sheath 3is used, these grooves or crevices 4; are closed by the sheath and therubber coating is applied to the outer surface of the sheath to which itadheres. rEhe saving in the quantity of insulation necessary to coat theconductor is therefore considerable. Again, in most of the rubber orrubber compounds used for insulating purposes there is present an excessof 'free sulfur, which attacks the surface of the conductor andtransforms a part of its copper content into copper sulfid, therebylessening the carrying capacity of the conductor. To avoid this eachindividual wire forming a conductor has heretofore been coated with tin.Where the sheath is used Patented July 3, 1917.

its exterior surface is alone tinned, which is a more economicalconstruction.

Where paper or cambric tape is used instead of rubber, as the insulatingcoating, and applied directly to the conductor the oil or other liquidhaving insulating propproperties thereby decreased. On 'the other handif the sheath 3 is used, since the joints between the overlapping `edgesare practically liquid-tight, it will prevent any of the insulatingliquids from being absorbed by the conductor, and they will thereforeremain distributed throughout the layers of the paper or cambricinsulation even after the cable has been in use for a considerableperiod of time.

Referring now to the construction shown in Fig. 3 which is that of thestandard type of sector cable consisting of three conductors 5, each ofwhich is, in cross section,

shaped to conform to a sector of acircle. Each of the conductors 5 isincased in a flexible sheath 6 similar to the one described, over whichis applied the coating T of insulation consisting of strips of papertape wound spirally around the sheath, the paper tape being impregnatedwith suitable insulating oils or other liquid compounds. The completecable is inclosed in .a lead sheath 8 as is the usual construction. Hereagain the flexible sheath 6 is of particular utility. The twisted wires5 forming the exterior of the sector are separated more at the sharpcorners 9 and 10 of a sector than on the sides of the sector, since theyare bent more abruptly at these points.

-When the paper tape is applied directly to the conductor, ridges andintervening grooves are formed in the first layers of paper tape, due toits Contact with these separated'wires, and when the other layers ofinsulating tape are applied over these, the ridges will be graduallyless pronounced. In the formation of a sector cable of this character itis necessary, however, in forming the cable, to impart a slight twist toeach conductor and its insulation. This twisting of the strands causesthe ridges in the layers of paper tape surrounding the conductor tobecome inore pronounced and the portions of the layers between theridges to form into grooves which increase in depth in the outer layersof the insulation, where the so-called wrinkling is very pronounced. Airgaps will therefore be formed in the insulation when two conductors arefitted against each other in the completed cable. With low tensioncables these air gaps are immaterial, but in high tension cables theyare regarded dangerous since they weaken the insulation and henceincrease the liability of the insulation breaking down across one of theairgaps upon a static discharge from one conductor to another. If thesheath 6 is used, and the paper tape is wound upon the same, theformation of the initial ridges in the paper tape is prevented and theformation of the deep grooves by the twisting of the conductors istherefore avoided, since the distortion in the coating of insulationwill occur equally and form minute wrinkles throughout its entire lengthrather than form the deep grooves which are occasioned by the initialformation of ridges in the layers of tape which surround the conductor.

Inhigh tension work the sheath is also of importance, since it preventsfa static discharge from any of the conductors of the cable. As isclear, in order to have a static discharge from a high tension cable itis necessary that the conductor or Wire be bent rather sharply toprovide a point at which the discharge may occur. In thevordinarytwisted conductor of vcircular cross section, since the twist impartedto. 'thel individual wires of the cable is practically uniform, thisstatic discharge is not liable to occur at any particular point alongthe len th of the conductor Wire. However, in the ormation of sectorcables, since the conductorlis of a sector-like shape, i. e., triangularrather than circular in cross section, the wires as theypass over thesharp corners 9 and 10 of the sector, are bent more sharply than atother points along their length. This sharp bend has been considered bysome as of suicient sharpness to form a point at which a staticdischarge of electricity is likely, but where a copper sheath is usedany liability of a discharge is entirely prevented, since the smoothexterior surface of the sheath provides no points at which the staticdischarge may occur, and the discharge can not take place from theconductors when incased within such a sheath.` A

Another advantage arising from the use of the sheath is that thebird-caging of any type of a conductor is prevented at all times. lt isobvious that in handling a conductor, especially where lateral pressureor compression is applied to a length of cable before .the insulation isapplied the wires are liable to separate more or less and buckle, whichis commonly referred to as bird-caging. ln applying some forms ofinsulation it has therefore been necessary to temporarily tape theconductor before the insulation is applied. The sheath 6 acts as aneicient substitute for this tape and will prevent individual wires ofthe conductor l:from separating or leaving their fixed position withinthe conductor.

@their advantages of a metallic sheath of character with specific typesof cables not specifically referred to herein, will be obvious to thoseskilled in the art, and l do not Wish to be limited to any particulartype of cable but only by the scope of the appended claims.

I claim:

1. An insulated electric cable comprising a conductor composed of aplurality of bare Wires, a relatively stili metallic ribbon Woundspirally around said Wires to break joints, said ribbon beingelectrically conductive and mechanically binding the Wires together, anda layer of insulation applied directly to said ribbon.

2. An insulated electric cable comprising a conductor composed of aplurality of bare Wires, a relatively Stii'l1 metallic ribbon Woundspirally around the Wires to break joints, said ribbon beingelectrically conductive and mechanicallyv binding the Wires together,and a layer of insulation composed of tape Wound spirally around saidribbon.

3. An insulated electric cable comprising a conductor composed of aplurality of bare Wires twisted together in the direction of theirlength, a relatively stiii'f metallic ribbon Wound spirally around theWires to break joints forming a substantially smooth sheath inclosingsaid Wires and mechanically binding the wires together, said ribbonbeing of electrically conductive material, and a layer oi' insulationapplied directly to said ribbon.

4. ln an insulated electric cable, a conductor substantiallysector-shape in cross section and composed of a plurality of individualbare Wires, a exible metallic sheath' surrounding the conductorcomprising a sti metallic ribbon bound spirally around said conductor tobreak joints, and a coating` of insulation applied to said sheath.

A 5. In an electric cable, a plurality of conductors substantiallysector-shaped in cross section and each composed of a plurality of bareWires, a flexible sheath surrounding each conductor comprising acurrent-carrying sti-' metallic ribbon bound spirally around the Wiresof a conductor, a coating of insulation applied to each conductor, thesaid sector-shaped conductors being arranged to form a cable ofsubstantially cir-1 cular cross section, and an outer layer ofinsulation common to all of the conductors.

ln Witness whereof l subscribe my signature in the presence of twowitnesses.

LE ROY CLARK.

Witnesses:

HENRY MONKLEY, WM. M STOCKBRIDGE.

